1. Field of the Invention
The present invention relates to a particle-dispersed thin film composed of particles having an improved crystalline orientation and dispersedly formed on a matrix, to a granular magnetic thin film using the same, and to production processes of these thin films.
2. Description of the Related Art
Studies on granular ferromagnetic thin films each comprising fine ferromagnetic particles of nanometer order dispersed on a nonmagnetic matrix have been reported. In recent studies, thin films each composed of fine crystalline particles of cobalt formed on a carbon matrix have been reported as probable and hopeful candidates as materials for ultrahigh density magnetic recording media.
In addition, as a material providing tunneling giant magnetoresistance effect (magnetoresistive effect), a granular thin film of a Co--Al--O system alloy based upon cobalt formed by sputtering is known to have a high resistance and excellent soft magnetic properties.
These materials having magnetoresistance effect are generally formed by dispersing ferromagnetic particles in a nonmagnetic electric conductive matrix, and provide change of the electric resistance in accordance with a variation of an external magnetic field. The materials are believed to have magnetoresistance effect depending on the spin of conductive electrons in an interface between the matrix and dispersed particles, and an improved magnetoresistance ratio is believed to be obtained by increasing dispersed particles in number while maintaining the dispersed particles fine in size. Accordingly, demands have been made to develop techniques to disperse fine ferromagnetic particles in a nonmagnetic electric conductive matrix.
As an example of a production process of such a particle-dispersed magnetoresistive substance, there is known a process of forming, on a substrate, an alloy film composed of a nonmagnetic electric conductive element and a ferromagnetic element having an extremely small mutual solubility to the nonmagnetic electric conductive element, heating the film after film-formation so as to dispersedly separate ferromagnetic particles. A process of forming discontinuous ferromagnetic particles onto a substrate by sputtering, and adhering a nonmagnetic thin film on the substrate and particles is also known.
The aforementioned process, however, cannot be applied when the nonmagnetic electric conductive element has any mutual solubility to the ferromagnetic material. Further, even if fine particles of nanometer order could be separated in a matrix, when the element composing the matrix and the element composing the particles have a little mutual solubility to each other, a part of the particles are absorbed by the matrix so as to fail to enhance the particle concentration. In addition, when the quantity of ferromagnetic material is increased simply to complement decrease of the particle concentration, a ferromagnetic material phase can frequently form giant particles or a continuous phase. Therefore, dispersed fine particles in a high concentration cannot be obtained.
In the production of the aforementioned particle-dispersed magnetoresistive material, if the crystalline orientation of each of the dispersed ferromagnetic particles can be controlled to a fixed direction, there is possibilities of imparting magnetic anisotropy and of giving a thin film having an satisfactory magnetoresistance effect. Under the present circumstances as mentioned above that fine ferromagnetic particles cannot be dispersed in a high density, however, the crystalline orientation of each of the particles cannot nearly be controlled.